Recent work by one of the present investigators has shown that experimentally induced impairment of 5-HT synthesis in rat brain initiates a persistant elevation of blood pressure. This observation supports the proposition of a causal role for the CNS in the genesis of essential hypertension. We will test the hypothesis that endogenous biogenic amines (NE and 5-HT) mediate many of the physiological functions of the brain stem vasomotor areas and that disturbances in biosynthesis or metabolism lead to significant changes in blood pressure. Agents which interfere with synthesis or metabolism will be applied directly to brain stem vasomotor areas of the cat by intraventricular (4th cerebral) injection, and chronic measurements of blood pressure and heart rate will be made. These experiments are designed to produce an experimental model of hypertension of CNS origin in a species which is suitable for both neurophysiological investigation of the CNS and for cardiovascular studies. Pharmacologic agents which act in the CNS to alter blood pressure, heart rate and baroreceptor reflex will be used in neurophysiological experiments to analyze the organization of brain stem vasomotor areas. With these agents we hope to establish the relation between changes in neuronal activity occurring in the vasomotor areas and changes in the function of the heart and peripheral blood vessels.